1. Field of the Invention
The present invention pertains to an improved process for producing a carbonaceous pitch product having a mesophase content ranging from about 50 to 100 percent, which is suitable for carbon fiber manufacture. More particularly, the invention relates to a process for making mesophase containing pitch capable of producing high strength carbon fibers, by contacting a feedstock with an oxidative gas at an elevated temperature to prepare an isotropic pitch and thereafter solvent fractionating the isotropic pitch to recover a mesophase pitch product suitable for carbon fiber manufacture.
2. The Prior Art
In recent years extensive patent literature has evolved concerning the conversion of carbonaceous pitch feed material into a mesophase-containing pitch which is suitable for the manufacture of carbon fibers having desirable modulus of elasticity, tensile strength, and elongation characteristics.
U.S. Pat. No. 4,209,500 (issued to Chwastiak) is directed to the production of a high mesophase pitch that can be employed in the manufacture of carbon fibers. This patent is one of a series of patents pertaining to a process for producing mesophase pitches suitable for carbon fiber production. Each of these patents broadly involves heat treating or heat soaking the carbonaceous feed while agitating and/or passing an inert gas therethrough so as to produce a more suitable pitch product for the manufacture of carbon fibers.
As set forth in the Chwastiak patent, earlier U.S. Pat. Nos. 3,976,729 and 4,017,327 issued to Lewis et al involve agitating the carbonaceous starting material during the heat treatment. The use of an inert sparge gas during heat treatment is found in U.S. Pat. Nos. 3,974,264 and 4,026,788 issued to McHenry. Stirring or agitating the starting material while sparging with an inert gas is also disclosed in the McHenry patents.
U.S. Pat. No. 4,277,324 (Greenwood) discloses converting an isotropic pitch to an anisotropic (mesophase) pitch by solvent fractionation. Isotropic pitch is first mixed with an organic fluxing solvent. Suspended insoluble solids in the flux mixture are then removed by physical means, such as, filtration. The solids-free flux liquid is then treated with an antisolvent to precipitate a mesophase pitch. The patent further discloses heat soaking the isotropic pitch at 350.degree. C. to 450.degree. C. prior to solvent fractionation.
U.S. Pat. No. 4,283,269 (Greenwood) discloses a process similar to that of 4,277,324 except that the heat soaking step is carried out on the fluxed pitch.
Japanese Patent 65090/85 discloses heating a carbonaceous feed to 350.degree.-500.degree. C. in the presence of an oxidizing gas to prepare a mesophase pitch.
U.S. Pat. No. 4,464,248 (Dickakian) discloses a catalytic heat soak preparation of an isotropic pitch which is then solvent fractionated to produce a mesophase pitch.
U.S. Pat. No. 3,595,946 (Joo et al) and U.S. Pat. No. 4,066,737 (Romavacek) call for the use of an oxidative reactive material, such as air to produce a heavy isotropic pitch which is used to make carbon fibers.
U.S. Pat. No. 4,474,617 (Nemura et al) describes treating low mesophase content pitch with oxidizing gas at a temperature of 200.degree. to 350.degree. C. to produce an improved carbon fiber.
Thus, the art shows that it is known to heat soak a feed to form an isotropic pitch which yields mesophase pitch on solvent fractionation.